Road congestion is a common problem on modern roadways. To relieve or prevent congestion many levels of government encourage car pooling. One common mechanism for encouraging car pooling is designating one or more lanes on a multilane roadway as “high occupancy” lanes, meaning they can only be used by vehicles containing more than a minimum number of occupants.
Another mechanism that can be used when trying to encourage car pooling on toll highways is “high occupancy tolling”, which means those vehicles that meet the threshold minimum number of occupants pay a lower toll amount than those vehicles that do not. Accordingly, drivers are encouraged to car pool because they will enjoy reduced toll charges.
A difficulty arises in determining how to charge differentiated toll amounts. In the context of a gated toll highway, where each vehicle must stop at a toll booth and present payment, it is easy for the toll booth operator to determine the number of occupants and charge the appropriate toll amount. However, most toll roadways are now at least partly electronic. In some cases, the toll roadways have no gated toll lanes because the system is entirely electronic. These may be referred to as “open road” electronic toll collection systems.
Electronic toll collection systems conduct toll transactions electronically using RF communications between a vehicle-mounted transponder (a “tag”) and a stationary toll plaza transceiver (a “reader”). An example of an electronic toll collection system is described in U.S. Pat. No. 6,661,352 issued Dec. 9, 2003 to Tiernay et al. Another example is described in U.S. Pat. No. 6,219,613 issued Apr. 17, 2001 to Terrier et al. The contents of U.S. Pat. Nos. 6,661,352 and 6,219,613 are hereby incorporated by reference.
In a typical electronic toll collection (ETC) system, a set of antennas is disposed to cover the roadway with overlapping coverage zones. Each antenna broadcasts a wakeup or trigger RF signal within its coverage zone. A tag on a vehicle passing through the coverage area or zone detects the wakeup or trigger signal and responds with its own RF signal. The tag responds by sending a response signal containing information stored in memory in the transponder, such as the transponder ID number. The response signal is received by the antenna.
The antennas operate under the control of a roadside reader that typically multiplexes in time or frequency to scan the roadway for transponders. When an antenna receives a response signal, the response signal is input to the reader, which may then conduct an electronic toll transaction, such as by debiting a user account associated with the transponder ID number. The reader may then cause the antenna to broadcast a programming RF signal to the tag. The programming signal provides the tag with updated information for storage in its memory. For example, the tag may be provided with a passage record update, which is information regarding the most recent toll plaza or entry/exit point traversed by the tag. For instance, a location, identifier or other information regarding the current reader may be recorded and/or a time stamp.
In U.S. Pat. No. 7,388,501, issued Jun. 17, 2008 to Tang et al., it was suggested that the ETC system may be leveraged to charge differentiated tolls based on high occupancy status of a vehicle. Tang et al. suggested that high occupancy status could be communicated from a vehicle to a roadside reader by sending a differently polarized transponder response signal to the roadside reader.
It would be advantageous to provide for an improved transponder, ETC system, and/or methods of operating the ETC system that facilitate high occupancy tolling.